1. Field of the Invention
The present invention relates to a method for controlling picture size in an LCD (Liquid Crystal Display) projector during a warm-up period. In particular, it is directed to a method for increasing a picture size from a minimum size to a predetermined size until the lamp of lightning source produces a normal output intensity as well as decreasing the picture size to a predetermined picture size when the electric power is turned off, so that the user may watch a picture on the screen as early as possible despite the insufficient lightning intensity from the lamp during a warm-up period.
2. Description of the Prior Art
Referring to FIG. 1, a conventional LCD projector includes: a keyboard 11; a microcomputer 12 for outputting PWM (Pulse Width Modulated) signals to an integrator 13 responsive to output signals of the keyboard 11, and at the same time controlling each part of the LCD projector according to the output signals of the keyboard 11, 11; an integrator 13 for integrating and converting the PWM signals transmitted from the microcomputer 12 into a direct current; a motor driving section 14 for supplying the current to the motor 15 responsive to the current value transmitted from the integrator 13; a gear 16 rotating in a normal or reverse direction responsive to the driving direction of the motor 15; a gear 17, meshed with the gear 16, for moving the projection lens 18 forwardly or backwardly in response to the rotation of the gear 16; a relay 20 for cutting off the electric power which is supplied to a lamp 22 of the LCD projector upon the control of the microcomputer 12; a relay 21 for cutting off the electric power supplied to a fan 23 upon the control of the microcomputer 12; and a display circuit section 24 for adjusting the brightness and contrast being outputted with respect to a control of the microcomputer 12.
Referring to FIG. 2, a conventional microcomputer 12 includes: a control logic section 121; a storing section 122 for storing a value corresponding to picture sizes and values of predetermined brightness and contrast of the picture by the user; a register 123 for temporarily storing increased or decreased value of the PWM signals in on- or off-state; and a generator 124 for outputting the PWM signals according to the value stored at the register 123. Outside the microcomputer 12 are provided a display circuit section 24 for adjusting a brightness and contrast of the picture according to control signals from the control logic section 121; and a keyboard 11 for inputting signals corresponding to the user's desired function, to the microcomputer 12.
For a derailed description of the conventional method for adjusting the zoom of the LCD projector, when a user sets the power key in a state of power-on via the keyboard 11, the microcomputer 12 enables the lamp 22 and the fan 23 to be in the on-state by mining on the relays 20 and 21, and outputs the PWM signals to the integrator 13 for increasing the picture size on the screen 19. The integrator 13 integrates the PWM signals supplied from the microcomputer 12, converts the integrated PWM signals to the direct currents values, and outputs the direct current values to the motor driving section 14. The motor driving section 14 provides the current equivalent to a current value inputted from the integrator 13. In addition, the gears 16 and 17 are rotated by the motor 15 thereby moving the projection lens 18 forward or backward according to the rotation direction of the motor 15. As a result, the picture size on the screen 19 increases or decreases. Thus, according to an input of the keyboard 11 for a rotation direction or an opposite rotation direction of the motor 15, the projection lens is moved forward or backward, so that the picture size on the screen 19 increases or decreases.
But, in the conventional LCD projector, in case of using a high brightness metal halide lamp, it can not have enough brightness for displaying the picture on the screen within 40 to 60 seconds from the time of the power-on. When a user wants a picture size to be 100 sq. inch, after turning on the electric power, he must wait for, e.g., for the lamp to heat up. Thus, the user can not use the screen display for approximately a minute because of the above described problems.